function getBigArray () {
  const a = [];
  for (i = 1; i <= 500000; i++) {
    a.push(i);
  }
  return a;
}

window.onload = function () {
  const a = getBigArray();
  new VirtualScroll({
    el: document.getElementById('content'),
    list: a,
    itemGenerator: function (prop) {
      const el = document.createElement('div')
      el.innerHTML = prop.index;
      return el;
    },
    itemHeight: 40
  })
}